Influence of unilateral castration and increased plane of nutrition on sexual development of Holstein bulls. I. Growth and sperm production

Re-stimulation of testicular function in GnRH-vaccinated stallions by daily GnRH agonist treatment

In stallions temporarily not intended for breeding, reversible suppression of testicular function by vaccination against GnRH can be of interest. In the present study, effects of GnRH agonist treatment on the resumption of testicular function after GnRH vaccination were investigated. Testis size, testosterone release, semen characteristics and behavior were evaluated. We hypothesized that GnRH agonist treatment would restore testicular function. Shetland stallions were assigned to an experimental and a control group (n = 6 each). Experimental stallions were GnRH-immunized twice, four weeks apart. Ejaculates for semen analysis and blood for analysis of testosterone concentration and GnRH antibody titers were collected. Each experimental stallion was hemicastrated together with an age-matched control animal when testosterone concentration decreased below 0.3 ng/mL. Three weeks thereafter, daily treatment with the GnRH agonist buserelin was initiated (4 μg/day for 4 weeks followed by 8 μg/day). The remaining testicle was removed when testosterone concentration exceeded 0.5 ng/mL in vaccinated stallions. Time from exposure to a mare until mounting increased in GnRH-vaccinated stallions and decreased with buserelin treatment. Total sperm count decreased after vaccination but increased only slightly in response to buserelin. Sperm motility and percentage of membrane-intact spermatozoa decreased after vaccination and returned to pre-vaccination values with buserelin treatment. Testosterone concentration and testis volume decreased after GnRH vaccination and started to increase with buserelin treatment. In conclusion, the downregulation of testicular function by GnRH vaccination can be counteracted with buserelin. This approach may be useful in GnRH-vaccinated stallions with prolonged suppression of testicular function.

Bayesian Linear Regression Modelling for Sperm Quality Parameters Using Age, Body Weight, Testicular Morphometry, and Combined Biometric Indices in Donkeys

Simple Summary

The prediction of sperm output and other reproductive traits based on testicular biometry is an important tool in the reproductive management of stallions. Nevertheless, corresponding research in donkeys remains scarce. Several donkey breeds in Europe face a compromising threat of extinction, which has been accelerated by the low renovation of populations and their inbreeding levels. Although research on female reproductive physiology has made crucial advances, much less is known about the physiology of the male. In the present work, two Bayesian models were built to predict for sperm output and quality parameters in donkeys. Models included combinations of age as a covariate and biometric and testicular measurements as independent factors. Results evidenced that the goodness-of-fit was similar for both models—hence, the combination of biometry and testicular factors presented improved predictive power. The application of these models may assist in the process of making decisions in respect to the reproductive/biological, clinical, and selection handling of the animals.

Abstract

The aim of the present study is to define and compare the predictive power of two different Bayesian models for donkey sperm quality after the evaluation of linear and combined testicular biometry indices and their relationship with age and body weight (BW). Testicular morphometry was ultrasonographically obtained from 23 donkeys (six juveniles and 17 adults), while 40 ejaculates from eight mature donkeys were analyzed for sperm output and quality assessment. Bayesian linear regression analyses were considered to build two statistical models using gel-free volume, concentration, total sperm number, motility, total motile sperm, and morphology as dependent variables. Predictive model 1 comprised the covariate of age and the independent factors testicular measurements (length, height and width), while model 2 included the covariate of age and the factors of BW, testicular volume, and gonadosomatic ratio. Although goodness-of-fit was similar, the combination of predictors in model 1 evidenced higher likelihood to predict gel-free volume (mL), concentration (×10⁶/mL), and motility (%). Alternatively, the combination of predictors in model 2 evidenced higher predictive power for total sperm number (×10⁹), morphologically normal spermatozoa (%), and total motile sperm count (×10⁹). The application of the present models may be useful to gather relevant information that could be used hereafter for assisted reproductive technologies.

Effects of unilateral castration on morphologic characteristics of the testis in one-, two-, and three-year-old stallions

The effects of unilateral castration on testicular compensatory hypertrophy were measured in 12 Morgan stallions, four each at one, two, and three years of age. They were randomized within age to intact (IN) or unilaterally castrated (UC) groups. Allotment and surgery were in January 1983 and total castration was in June 1983, 150 d after unilateral castration. Testis weight increased linearly with age (P < 0.01) and was increased by unilateral castration (P < 0.07). Epididymal weight also increased linearly with age (P < 0.05) and was heavier in UC animals (P = 0.15). Tubule diameter (P < 0.10) and epithelial height (P < 0.03) were greater in UC than in IN stallions. In conclusion, testes of stallions underwent compensatory hypertrophy after unilateral castration.

Photoperiodic regulation of compensatory testicular hypertrophy in hamsters

In mammals, removal of one testis results in compensatory testicular hypertrophy (CTH) of the remaining gonad. Although CTH is ubiquitous among juveniles of many species, laboratory rats, laboratory mice, and humans unilaterally castrated in adulthood fail to display CTH. We documented CTH in pre- and postpubertally hemi-castrated Syrian and Siberian hamsters and tested whether day length affects CTH in juvenile and adult Siberian hamsters. Robust CTH was evident in long-day hemi-castrates of both species and was preceded by increased serum FSH concentrations in juvenile Siberian hamsters. In sharp contrast, CTH was undetectable in short-day hemi-castrated Siberian hamsters for several months and only made its appearance with the development of neuroendocrine refractoriness to short day lengths; serum FSH concentrations of juveniles also did not increase above sham-castrate values until the onset of refractoriness. Long-day hemi-castrated Siberian hamsters with hypertrophied testes underwent complete gonadal regression after transfer to short days, albeit at a reduced rate for the first 3 weeks of treatment. Blood testosterone concentrations of adult hamsters did not differ between long-day hemicastrates and sham-castrates 9-12 weeks after surgery. We conclude that CTH is suppressed by short day lengths in Siberian hamsters at all ages and stages of reproductive development; in short day lengths, but not long day lengths, the remaining testis produces sufficient negative feedback inhibition to restrain FSH hypersecretion and prevent CTH.

Sertoli cells in the boar testis: changes during development and compensatory hypertrophy after hemicastration at different ages

Changes in Sertoli cell numbers and testicular structure during normal development and compensatory hypertrophy were assessed in crossbred Meishan x White Composite males. Boars were assigned at birth to unilateral castration at 1, 10, 56, or 112 days or to remain as intact controls through 220 days. The first testes removed were compared to assess testicular development. At 220 days, testicular structure was evaluated in boars representing the 25% with the largest (Lg) testis and the 25% with the smallest (Sm) testis in each treatment group. The number of Sertoli cells per testis reached a maximum by Day 56 in Sm testis but not until Day 112 in Lg testis boars, indicating a longer duration of Sertoli cell proliferation in Lg testis boars. Unilateral castration of Lg testis boars on Days 1, 10, 56, and 112 caused the weight of the remaining testis to hypertrophy by 149%, 135%, 119%, and 120%, respectively, and total sperm production to increase to 127%, 128%, 97%, and 106%, respectively. However, Sertoli cell numbers changed little in hemicastrate boars. In Lg testis boars, compensatory hypertrophy primarily involved proliferation of Leydig cells and expansion of existing Sertoli cells with little increase in Sertoli cell numbers, but in Sm testis boars, it involved expansion of existing Leydig and Sertoli cells without increase in cell numbers. These results indicate that Lg and Sm testis boars display intriguing differences during both development and compensatory hypertrophy, and they identify a unique animal model for further studies of factors that program and control Sertoli cell proliferation.

The influence of duration of photoperiod and hemicastration on growth and testicular and endocrine functions of boars

Yorkshire boars were used to evaluate the influence of duration of photoperiod and hemicastration on growth and testicular and endocrine functions. At 10 wk of age, 5 hemicastrate (HC) and 5 intact (I) boars were assigned to either 8 or 16 hr of light daily until 6 mo of age. Body weights were recorded biweekly throughout the experiment. Venous cannulae were placed in all boars at 6 mo of age, and serum was collected at 30 min intervals from 0800 to 2000 hr. Gonadotropin releasing hormone (GnRH) was infused at 2000 hr (50 micrograms) and at 2030 hr (250 micrograms), and samples of serum were collected until 2400 hr. The following day, all boars were castrated, and the weights and sperm content of the testes and epididymides were determined. At castration, all pigs were given implants containing testosterone. Two weeks later, pigs were again canulated, and serum was obtained at 15 min intervals for 2 hr. Growth of boars was not significantly affected by duration of photoperiod or number of testes. Duration of photoperiod did not affect weight or sperm content of testes or epididymides. Hemi-castrated boars had greater testicular (P less than .01) and capita-corpora (C-C) epididymal weights (P less than .05) and more testicular and C-C sperm (P less than .01) per testis. Neither average concentrations of luteinizing hormone (LH) nor number and amplitude of pulses of LH were affected by photoperiod treatment. However, HC boars had greater average concentrations of LH (P less than .05) than I boars (.71 +/- .05 vs .52 +/- .05 ng/ml). Hemicastrated boars in 16 hr light daily had greater concentrations of FSH in serum (P less than .05) than 8I, 8HC, and 16I boars. Intact and HC boars had similar concentrations of prolactin (PRL) and testosterone. Similarly, concentrations of PRL and testosterone were not affected by duration of photoperiod. Secretion of LH and testosterone after treatment with GnRH was not significantly affected by duration of photoperiod. In general, HC boars released more LH in response to GnRH treatment than I boars. Concentrations of LH were greater (P less than .05) in HC than I boars at .5, 1, 2, and 3 hr after GnRH and tended (P less than .10) to be elevated at 1.5, 2.5, 3.5 and 4 hr after GnRH. The FSH response to GnRH was greater (P less than .05) for 16HC than 8I, 8HC, or 16I boars.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of unilateral castration on serum luteinizing hormone, follicle stimulating hormone, and testosterone concentrations in one-, two-, and three-year-old stallions

The endocrine control of compensatory hypertrophy was investigated in 12 Morgan stallions, four each at one, two and three years of age. Half were assigned to be unilaterally castrated (UC) in January and half to remain intact (IN). Nine blood samples were taken from each stallion at half-hour intervals 30, 90, and 150 d after unilateral castration for radioimmunoassay of serum concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone. Mean serum LH concentration was greater (P<0.06) in UC than IN stallions; however, the difference was greatest at 30 d and least at 150 d. Serum LH was greater (P<0.01) in two- and three-year-olds than in one-year-olds. The mean log(10) for serum FSH concentration was greater (P<0.06) in UC than IN stallions. Mean serum testosterone concentrations were similar in UC and IN stallions for all sample days, suggesting that the single testes of the UC stallions produced as much testosterone as the two testes of the IN stallions. Two- and three-year-old stallions had greater (P<0.01) serum testosterone than one-year-old stallions. Unilateral castration of stallions was associated with a significant increase in serum LH and FSH concentrations and, perhaps, higher intratesticular testosterone, which may explain, in part, the compensatory hypertrophy noted in the remaining testis.

Testosterone, luteinizing hormone, follicle stimulating hormone, and prolactin response to unilateral castration in prepubertal Holstein bulls

Hemicastration of Holstein bulls at 3 months of age resulted in increased (P<0.005) testicular weitht and testis sperm cell content at 330 days after treatment, but did not alter sperm cell concentration in the remaining hypertrophied testis. Radioimmuroassay of blood hormones at 1, 6, 12, and 24 weeks after treatment revealed that unilateral castration did not alter (P>0.1) basal levels or GnRH response profiles of either LH or testosterone compared to intact bulls. Hemicastration caused FSH to be elevated (P<0.01) compared to intact bulls at all sampling periods in both unstimulated and GnRH stimulated bulls. Prolactin varied with season and was greater (P<0.001) in hemicastrated bulls than in intact bulls at 1 and 6 weeks after treatment. Results indicate that unilateral castration at 3 months of age caused testicular hypertrophy of both steroidogenic and gametogenic function and this phenomena may be triggered by increased FSH or prolactin secretion, or both. Further, results indicate different testicular regulation mechanisms exist for pituitary LH and FSH release in bulls.